Download Benthic Ecology and Demersal Resources

Benthic Ecology and Demersal
Resources
Dr. Dattesh V Desai
CSIR-NIO, Dona Paula, Goa
[email protected]
Divisions of the Marine Environment
Benthos
Community of organisms - live on, in, or near the seabed, also
known as the benthic zone
Live in or near marine sedimentary environments, from tidal pools
along the foreshore, out to the continental shelf, and down to the
abyssal depths
Most organisms in the benthic zone are scavengers or detritivores
Ecology
• Factors regulating the distribution and abundance of organisms
in the ocean
• Influence of physical and chemical parameters on organisms in
the various ecosystems
• Ecosystem - includes the living (biotic) and non-living (abiotic)
portions of the environment.
– e.g., coral reefs, estuary, rocky intertidal habitats,
Mangroves, etc.
Benthic Ecology
Environmental factors
influencing benthos include
-temperature
-salinity
-pressure
-nutrients
-dissolved gases
-currents
-light
-suspended sediments
-substrate (bottom
material)
-river inflow
-tides and waves.
Benthic Lifestyle
•
•
•
•
•
Benthos
Epibenthic
Burrowers
Borers
Infaunal, Semiinfaunal
• Benthic swimmers
• Interstitial
Classification – Based on size
Macrobenthos - The larger, more visible benthic organisms –
greater than or equal to 0.5mm (shortest dimension)
e.g. Polychaete worms, bivalves, echinoderms, sea anemones, corals, sponges,
sea squirts, turbellarians, larger crustaceans (crabs, lobsters, etc)
Meiobenthos - Tiny benthic organisms that are less than 0.5mm
but greater than 0.1 mm in size.
e.g. nematodes, foraminiferans, water bears, gastrotriches and smaller crustaceans
such as copepods and ostracodes, amphipods.
Microbenthos - Microscopic benthic organisms that are less
than 0.1 mm in size.
e.g. Some examples are bacteria, diatoms, ciliates, amoeba, flagellates.
Classification – Based on feeding mode
•
•
•
•
•
Suspension feeders
Deposit feeders
Herbivores (macroalgae or microalgae)
Carnivores
Scavengers
Classification – Based on feeding guild
Herbivores – Eat non-microscopic plants (seaweeds, sea grass)
e.g. Urchins, Benhtic Fishes
Carnivores – Eat other animals e.g. starfish, crabs, fishes, worms
etc.
Scavengers – Feed on carcasses and remains of other animals
and plants
Many deposit feeders are scavengers - Fish, sea stars, snails,
cephalopods, crustaceans are important predators and
scavengers.
Food sources for benthos
Algae and organic runoff from land or from the pelagic zone
In coastal waters and other places where light reaches the bottom,
benthic photosynthesizing diatoms can proliferate.
Filter/Suspension Feeders – Sponges and bivalves dominate hard,
sandy bottoms
Active Suspension Feeders – Draw particles towards the mouth parts by
creating a current
Passive Suspension Feeders – Protrude a feeding organ & collect
particles as they are deposited
Deposit feeders – Ingest sediment and use organic matter and
microbial organisms in the sediment as food.
Optimize their intake of food by adjustments of particle size to be
ingested and adjustment of gut passage time.
Classification - By type
Zoobenthos
Zoobenthos comprises the animals belonging to the benthos
Phytobenthos
Phytobenthos comprises the plants belonging to the benthos, mainly benthic
diatoms and macroalgae (seaweed)
By location
Epibenthos
Epibenthos lives on top of the sediments.
Hyperbenthos
Hyperbenthos lives just above the sediment.
Suspension Feeders
• Feed on small particles
• Passive versus active suspension feeders
Bivalve, x-section
Polychaete Serpula
Barnacle
Suspension Feeders
Sea squirt Styela montereyensis
Passive suspension feeding mechanism
Deposit Feeders
• Feed upon sediment, within the sediment or at
sediment surface
• Head-down deposit feeders feed within the sediment
at depth, usually on fine particles, defecate at surface
• Surface browsers - Feed on surface microorganisms
such as diatoms
• Feeding activity accelerates microbial attack - grazing
stimulates microbial metabolism, resulting in tearing
apart of organic particles
Deposit Feeders
Within Sediment Tentacle feeding
bivalve
Surface tentacle
feeding polychaete
Within sediment or deep
feeding Polychaete
Surface deposit-feeding
siphonate bivalve
Surface feeding
Amphipod
Deep feeding polychaete
Herbivores
Polychaete Nereis vexillosa
Parrot fish
radula
Chiton
Urchins
Carnivores
Bivalve Cuspidaria
oystercatcher
Gastropod Nucella
Polychaete
Glycera
Crab Callinectes sapidus
Cellulose feeder
Bivalve Teredo
foot
Greatly elongated mantle
Obtains nitrogen
with symbiotic
nitrogen fixing bacteria
Burrowing in sediment
• Burrowers use hydromechanical and mechanical
digging mechanisms to move through the sediment
• Hydromechanical burrowing - combines muscle
contraction working against rigid, fluid filled chamber
(skeleton)
• Form penetration anchor first
extension of body into sediment
to
allow
further
• Form terminal anchor to allow pulling of rest of body
into the sediment
Burrowing in sediment
Biogenic structures - burrowing and processing
of sediment affects sedimentary structures
1. Burrowing in mud increases water
content of sediment
2. Increases grain size (pellets)
3. Alters vertical and 3-D mechanical structure
Interstitial animals
• Live in the pore waters of sediment- in sand grains
• Belong to many taxonomic groups
• Elongate, wormlike form, in order to move through
tight spaces
Harpacticoid
Polychaete
Hydroid
Gastrotrich
Opisthobranch
gastropod
Interstitial organisms
Soft-Sediment Microzone
• Microbial types also vary with depth below the
sediment water interface
• Towards the surface, aerobic bacteria dominate
(energetically most efficient to use oxidation)
• Deeper, bacteria present that can live in the absence
of oxygen and can produce energy through various
chemical means
Grain Size vs Feeding Type
• Sandy bottoms
– High water flow
– Shallow waters
Suspension feeders
• Muddy (clay-silt) bottoms
– Low currents
– Deep Ocean
Deposit feeders
Suspension
feeders
%
Deposit
feeders
Clay
Sand
Sediment Stabilizing vs Destabilizing organisms
Ecological Roles
1. Help stabilize the sediment
2. Prevents resuspension of sediments in water (water is
clearer)
3. Binds substratum, reduces turbidity, and reduces
erosion
4. Sediment accumulation slows velocity of incoming
water
5. Food for many organisms
6. Refuge for many organisms
Deep Sea Benthos
• Characteristics of many deep sea benthos are:
– low activity levels
– slow growth & development; long lives
– the deeper the water, the decrease in number and diversity
of benthic organisms
– Late reproductive maturity
• Some common adaptations are:
– Bottom feeders
– high water content in their bodies to deal with the pressure
– bioluminescence to attract food and mates & large eyes
– Long sharp teeth or fangs (act like spears)
– Large flexible stomachs
Deep Sea Benthos
Physiology
 Low metabolic rate and activity level
Ecological
 Long lived species
 Slow colonization rates
 Low population densities, but high species diversity
Deep-Sea Benthic Environments
Characterized by:
Low availability of food
No light, no photosynthesis
Falling remains of dead organisms, decaying
organic matter
Low (0-2°C), relatively constant temperature
High pressure (400-500 times atmospheric)
Deep-Sea Benthic Environments
What supports of life around hydrothermal vents?
What is the energy source for this ecosystem?
Chemosynthesis
• Basis of life around deep sea hydrothermal vents is
chemosynthesis rather than photosynthesis
• Chemical energy rather than solar energy supports the
ecosystem
• Bacteria rather than plants are the primary producers
• Organisms must have adaptations to prevent sulfide from
poisoning oxygen binding site
Hydrothermal Vent Macrofauna: Worms
Vestimentiferan worms
(Riftia pachyptila )
Serpulid polychaete worms
Hydrothermal Vent Macrofauna: Bivalves
Giant clams
Mussels
(Bathymodiolus thermophilus)
Geol 104/BioES 154
Intertidal region
Spray or Splash Zone
Mostly
shelled
orgs
High Tide Zone
Middle Tide Zone
Low Tide Zone
Many
soft
bodied
orgs and
algae
Benthos in the Intertidal region
Community determinant factors
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•
•
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Larval Supply / Settlement
Physical Forcing
Competition
Predation
•High Diversity
•Low movement
•High adaptive mechanisms – Behavioral, Morphological,
Physiological
Sessile/Sedentary Invertebrates
Dispersal
Predation Food
Release of
Propagule
Settlement
Breeding
Adhesion
Growth
Temporary
Attachment
Development
Permanent
Attachment
Clam: Benthos or plankton?
Population connectivity of marine organisms
Connectivity: Ensuring linkages between sites through currents,
migratory species, larval dispersal
• Organisms distributed as many small breeding groups (populations)
• Pattern set by geography, hydrodynamics, and biology
• Populations interact through exchange of individuals (connectivity)
• May be isolated, a metapopulation, or a large, but subdivided
population
Understanding population connectivity to develop spatial management
methods for capture fisheries!!
Offshore
+
+
-
Time
Space
Scale of processes influencing the population
Population abundance
Relative importance of density dependent factors
Larval pool
Onshore
+
Physical & larval
transport processes
Local biotic interactions
& disturbance
Microhydrodynamic, behavioral &
substrate availability process
Determinants of larval pool
Determinants of settlement
Determinants of population abundance
So: Jesús Pineda, Oceanography of the Eastern Pacific, 1 (2000) 84-105
Benthic Population
Connectivity with different trophic levels -Important to take into
consideration the benthic population inhabiting within and
above the sediment
Demersal fishery - Sustained by benthic organisms
Benthic organisms - Release larvae into pelagic realm and how
larvae are dispersed and borough back to the recruitment site
to replenish the population is important from fishery perspective
How these are distributed over different type of sea bed and
particular season favors any particular group of organisms and
in turn these support specific fishery is an important issue
Resources
Measurement of secondary production - Essential to the
management of aquatic resources
Fish - Depend to a high degree upon zooplankton and
benthos for food
- Understanding the production processes of
invertebrates will facilitate management of fish stocks or
prediction of rates of fish production/ living resources
Food production, availability, and quality
• Community of heterotrophs can fix no more energy
than the amount made available to them by primary
producers.
• The rate of primary production must set the upper
limit for secondary production.
• Rates of production of benthos and zooplanklon are
positively related to food availability
• Rates of zooplankton and benthos production are
positively related to rates of primary production
Benthic-pelagic coupling
Nutrient exchange or benthic-planktonic coupling occurs
between bottom sediments and overlying water column
Main coupling factors
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•
•
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Organic matter input in surficial sediments
Resuspension process
Nutrient recycling
Contaminant sequestration
Organic matter input in surficial sediments
Main forcing factors
• Depth
Shallow sediments – High coupling; Deep Sediments - Low
coupling
• Decay rate of organic matter
• Settling velocity
• Disequilibrium between production and consumption in
surface waters
Resuspension processes
Mainly:
Sediment particles (Inorganic, Organic aggregates,
dead organisms)
Microphytobenthos
Either fixed on particles or free but resuspended
Macrophytes
The distal part of macrophytes is regularly cut by
waves and movements on rocks
Macrobenthic organisms
Either larval stages, or adults (Polychaetes).
Benthic-pelagic coupling
Euphotic layer
Organic Particulate Matter
CO2
Settling
Resuspension
Nutrient
recycling
NO3-, NH4+ ,
PO43-, Si(OH)4
Accumulation
WATER
COLUMN
SEDIMENT-WATER
INTERFACE
?Mineralization
SURFICIAL
SEDIMENT
Refractory
Organic Matter
Demersal Resources
Fish are a taxonomically and morphologically diverse group.
Broad feeding types: Filter feeders, Planktivores, Piscivores and
Benthic feeders.
Filter feeders - strain the water column indiscriminately for small prey, typically
phyto- and zooplankton.
Planktivores - Prey upon individual zooplankton, (Copepods, mysids and
gammarids)
Piscivores – Prey upon small fishes
Benthic, or bottom-dwelling - Include sturgeon, catfish, flounder
etc. Because of their habitat orientation, they feed primarily on
epibenthic organisms such as amphipods, bay shrimp, and
bivalves.
Demersal Resources
• Benthic animals play an important role in energy transfer as
they are utilized as prey by fish and larger crustaceans
• Benthic animals support important commercial and recreational
fisheries
• Clams, Oysters, Scallops and other molluscs; Lobsters, Crabs,
and Sea urchins are economically valuable benthic species
• Tube-building worms and amphipods can be important food for
- juveniles of economically and ecologically important fish
species
• Benthic surface-dwelling (epifaunal) communities support - sea
anemones, zoanthids (colonial anemones), sponges, hard and
soft corals, sea stars, lobsters, squat lobsters (galatheids),
shrimp and crabs
Disturbance to benthic ecosystems
Disturbance - “any relatively discrete event in time that disrupts
ecosystem, community, or population structure and changes
resources, substrate availability or the physical environment”
Disturbances - Organic enrichment and/or hypoxia change
benthic community composition.
Anthropogenic disturbances also include bottom trawling
Response strategies do not rescue an animal from a
disturbance, mortality will occur, resulting in altered community
composition
Impacts of trawling on the seabed and benthic
communities
• Destruction
or damage to structurally complex habitats
• Reduction of habitat heterogeneity and homogenisation
of subtly textured habitats
• Reduction in bioturbation
• Death and damage to infauna and epifauna
• Reduction in benthic species diversity
• Re-suspension of sediments
• Attraction of scavengers
• Declines in larger, slow growing species
• Increases in smaller, faster growing taxa
(Jennings and Kaiser 1998, Auster and Langton 1999, Collie et al. 2000a,b, Jennings et al. 2001, Kaiser et al. 2002,
Widdicombe et al. 2004, Kaiser et al. 2006, Hiddink et al. 2008).
Thank You